This invention relates to an improved annular wiper seal which is used to prevent the ingress of foreign material from the sea floor into a jacket leg or pile sleeve of a marine platform when driving a piling therethrough.
To secure a marine platform to the sea floor, a pile is usually driven through each of the jacket legs into the sea floor with the top of the pile being secured to the top of the jacket leg, typically, by welding shim plates in the annulus between the jacket leg and pile. If the marine platform also has pile sleeves, piles are usually driven through the pile sleeves into the sea floor. To secure the piles to the pile sleeves and to provide additional support between the piles and the jacket legs of a marine structure, the annuli between the piles and the pile sleeves and jacket legs are usually filled with grouting material.
When a platform is lowered to the sea floor, the jacket legs and pile sleeves will settle into the sea floor with debris from the sea floor being prevented from entering the jacket legs and pile sleeves by means of diaphragms installed on the bottom thereof. Subsequently, upon driving a pile through the jacket leg and pile sleeve when the diaphragm is ruptured, unless prevented, the inrush of debris from the sea floor and mud entrained in water will fill the annulus through the ruptured diaphragm. If the annulus between the pile and jacket leg and pile sleeve is filled with debris and mud, it is desirable to clean the annulus before the grouting thereof to insure filling of the annulus with grouting material and the proper bonding of the grouting material to the pile and jacket leg.
In many instances, an annular wiper seal is installed above the diaphragm to seal the annulus between the pile and jacket leg or pile sleeve to prevent the debris and mud from the sea floor rushing into the annulus when the diaphragm is ruptured by the pile being driven therethrough. When the annulus between the pile and jacket leg and pile sleeve is being filled with grouting material, the annular grout seal may also help support the grout column.
One typical type prior art annular wiper seal as described in U.S. Pat. No. 3,533,241 comprises an elastomeric wiper which is reinforced by means of layers of reinforcing cord therein extending from a point intermediate its inner periphery and outer periphery to its outer periphery, the layers being alternately wrapped about an annular reinforcing member having a circular cross-sectional shape retained within the outer periphery of the wiper. The wiper is secured to the jacket leg or pile sleeve by means of a pair of annular flat plates which protrude from the jacket leg or pile sleeve, each plate having a semicircular groove therein to receive a portion of the outer periphery of the wiper having the circular cross-sectionally shaped reinforcing member therein. The top annular flat plate of the pair of annular flat plates is secured to the jacket leg or pile sleeve by means of welding with the pair of annular flat plates being secured to each other by a plurality of threaded fasteners extending through apertures in the outer periphery of the pair of annular flat plates.
While this typical prior art seal is generally reliable in service, it requires careful wrapping of the layers of reinforcing cord about the annular circular cross-sectionally shaped reinforcing member during the wiper construction process, requires the machining of semicircular shaped grooves in the flat annular plates to receive the outer periphery of the wiper therein, and requires careful torquing of the threaded fasteners to prevent the wiper from being released from the annular flat plates when the pile is inserted and driven therethrough.
Another typical prior art annular wiper seal as described in U.S. Pat. No. 3,570,259 comprises a plurality of wire reinforcing members embedded in elastomeric material. The wiper is held in position in the jacket leg or pile sleeve by means of two annular bands which are welded in position and have an annular channel therein which receives the bent ends of the wire reinforcing members embedded in the elastomeric material. A separate pile guide member is welded in the jacket leg or pile sleeve above the wiper to guide the pile therethrough upon insertion.
While of relatively simple construction, the wiper requires the handling and accurate placement of a large number of wire reinforcing members during the wiper construction process. The wiper additionally requires the use of a separate pile guide member to prevent the pile from damaging the wiper or its securing means when a pile is being inserted therethrough, thereby requiring an extra welding operation to be performed during installation. Furthermore, once the pile has been inserted through the wiper and the reinforcing members plastically deformed, which will occur when the pile is not concentrically located within the wiper or when the pile is withdrawn from the wiper and reinserted therethrough, the wiper is no longer capable of sealingly engaging the periphery of the pile to prevent debris and mud from entering the annulus between the pile and the jacket leg or pile sleeve when the diaphragm is ruptured.
Yet another annular pile wiper as described in U.S. Pat. No. 4,181,454 comprises an elastomeric member having a reinforced peripheral portion which is perpendicular to the sealing portion of the wiper, the wiper being retained within the jacket leg or pile sleeve by upper and lower end shoes engaging the reinforced peripheral portion of the wiper and being welded to the interior of the jacket leg or pile sleeve.
While the wiper is simple to construct, its manufacture may involve costly molding dies.
Still yet another annular wiper seal as described in U.S. Pat. No. 4,183,698 comprises a portion of a combination diaphragm, grouting seal and wiper assembly installed on the lower end of a jacket leg of an offshore platform. The annular wiper seal comprises an elastomeric manifold which acts as a grout seal and pile wiper. The manifold is initially retained within a housing by a shiftable cage having shoulders thereon which protrude into the jacket leg of the platform. As the pile is driven through the jacket leg the pile engages the shoulders on the cage causing the cage to be driven through the diaphragm on the jacket leg with the diaphragm being severed by the cage and the end of the pile. When the cage has been shifted downwardly, the manifold expands into engagement with the pile thereby acting as a pile wiper during pile driving operations and subsequently as a grout manifold during grouting operations. In an alternative embodiment of the combination grout seal and pile wiper, the shiftable cage is eliminated with the reinforced periphery of the diaphragm retaining the manifold in its collapsed state. Upon inserting and driving a pile through the jacket leg, the pile shifts the diaphragm to allow the manifold to expand with the end of the pile severing the diaphragm.
While the combination of a grout seal and pile wiper may offer advantages over a separate pile wiper assembly and grout seal assembly installed on the jacket leg of an offshore platform, the combination grout seal and pile wiper may be damaged during pile insertion and driving operations and fail to perform either as a pile wiper or grout seal.